Support is requested fro a computer facility serving the group of principal investigators of NIH grants in projects of ultrastructural research and molecular biology. Emphasis is on projects in the areas of structural biology using the conventional electron microscope and computer tomography using the high voltage electron microscope. The range of biological structures encompassed by these projects include ribosomes and enzyme complexes, cilia, components of the mitotic apparatus, and whole cell reconstructions. The projects relate to issues of the fundamental structure of macromolecular complexes and organelles as well as to specific disease and developmental processes. Most of the computer-based components of these projects rely on the availability of raster graphics, large disk space and memory. The use of a shared facility is appropriate because the bulk of the existing software developed in-house has been written with a view towards accommodating a wide range of applications, and because such a facility leads to the most efficient utilization of resources.